The attacker, armed with two large knives, mowed down pedestrians with a car on Westminster Bridge, including schoolchildren, then rushed at the gates in front of the Houses of Parliament, stabbing Palmer before being shot dead by other officers.

Paramedics fought to save Palmer’s life, and that of his attacker, on the floor of the cobbled courtyard in front of Parliament, with Foreign Office minister Tobias Ellwood among those who rushed to help.

Speaking outside Scotland Yard on Wednesday night, acting deputy commissioner Mark Rowley, the Met’s senior anti-terror officer, said about 40 people had been injured, several - including two police officers - seriously, the Press Association reports.

Paying tribute to Palmer, a member of the Parliamentary and Diplomatic Protection Squad who had served the police for 15 years, Rowley said: “Today in Westminster we saw tragic events unfold and our thoughts are with those who lost loved ones, those who were injured and all those affected by this attack.

Hannah Mckay / Reuters
Four people, including the attacker, were killed in the incident

“One of those who died today was a police officer, PC Keith Palmer, a member of our parliamentary and diplomatic protection command. Keith, aged 48, had 15 years’ service and was a husband and father.

“He was someone who left for work today expecting to return home at the end of his shift, and he had every right to expect that would happen.”